As a rookie with the Atlanta Braves in 2011, Kimbrel was named their closer, and set an MLB record for saves by a rookie with 46. He was awarded the National League's 2011 Rookie of the Year Award.[1] On June 6, 2014, he recorded his 155th save to surpass John Smoltz as the Braves' all-time leader in saves. Kimbrel was traded to the San Diego Padres prior to the start of the 2015 season, and to the Red Sox before the 2016 season. He is known for the speed of his fastball, as well as his unique and intimidating pre-pitch stare.[2]

Kimbrel got his first call-up from the Gwinnett Braves on May 15, 2010, to replace the injured Jair Jurrjens on the roster.[4] He was called up for the second time in his career on June 4, 2010, to replace Takashi Saito, who was placed on the 15-day DL.[5] He earned his first major league save on September 19, 2010 against the New York Mets. Kimbrel's record for the 2010 season was 4–0, with one save and a 0.44 ERA in 202⁄3 innings. He recorded 40 strikeouts and 16 walks.[3] In the 2010 playoffs, he shut down the eventual World ChampionSan Francisco Giants on several occasions; he had 7 strikeouts in a total of 41⁄3 innings, appearing in all 4 games of the NLDS between the Giants and the Braves.

Kimbrel made the roster to start the 2011 season as the team's primary closer. He was successful in his first four save opportunities before blowing his first career save on April 21, 2011. On June 3, 2011 in a game versus the New York Mets, Kimbrel passed the record for most saves by a National League rookie before the All-Star break.[6] He is the fastest Braves pitcher to reach 100 career strikeouts, doing so in 591⁄3 career innings. His new record surpassed the previous record set by John Rocker in the 1998–1999 season, where it took Rocker 70 career innings to reach the 100 career strikeout mark.[7] On July 5, his 26th save matched Jonathan Papelbon's record for most saves by a rookie before the All-Star break.[8] On July 7, Kimbrel's 27th save of the year against the Colorado Rockies broke Papelbon's record.[9]

On July 22, 2011 in a game versus the Cincinnati Reds, Kimbrel broke the Braves rookie record for saves in a season (31).[10]

On August 9, 2011 in a game versus the Florida Marlins, Kimbrel tied the National League rookie record for saves in a season (36 by Todd Worrell of the St. Louis Cardinals in 1986). He broke that record on August 17 in a game versus the San Francisco Giants. On August 21, 2011, Kimbrel recorded his 100th strike out which coincided with his 39th save of the season and a string of 302⁄3 innings without yielding a run.[11][12] On August 23, 2011, Kimbrel recorded his 40th save, tying the rookie save record of Neftalí Feliz. He subsequently broke this record with his 41st save on August 31 with two strikeouts in a game against the Washington Nationals. At the time, he led the majors in saves and had not given up a run in his last 34 innings.[13] The following night September 1, 2011, Kimbrel surpassed Cliff Lee's record of thirty four scoreless innings with 342⁄3 scoreless innings for the longest scoreless streak in the majors in 2011.[14] He was named the NL Rookie of the Month and MLB Delivery Man of the Month for August 2011.[15][16] His scoreless inning streak came to an end after 381⁄3 innings, on September 9, 2011.[17]

The Braves season ended when he blew a save against the Philadelphia Phillies in the last game of the season. The loss knocked Atlanta out of playoff contention, completing a late-season collapse that squandered an early-September lead of 8½ games.[18] Kimbrel's mediocre September (4.76 ERA)[19] led to charges that manager Fredi González had overworked him over the course of the season.[20][21]

Kimbrel ended the season tied for the National League lead with 46 saves—shattering the previous rookie record of 40, set by Feliz in 2010—and led the Major Leagues with 127 strikeouts in 77 innings of relief.[22]

Kimbrel was thoroughly dominant throughout the 2012 season. He led the National League with 42 saves (in 45 opportunities) and Win Probability Added among pitchers. He struck out 116 batters in 622⁄3 innings, producing a K/9 rate of 16.7.[29] In so doing, he also became the first pitcher in history to strike out at least half the batters he faced during a season.[30] He also went to an 0–2 count on 56% of the batters he faced.[31] Kimbrel allowed only 3.9 hits and 2.0 walks per 9 innings he pitched, giving him a WHIP of 0.65 and a batting average against of .126. He finished with an ERA of 1.01.[29] He won the NL Rolaids Relief Man Award.[32] Kimbrel finished fifth in the 2012 National League Cy Young Award voting,[33] and eighth in the 2012 National League MVP voting.[34]

Kimbrel began the 2013 season with three blown saves during his first nine save opportunities, tying his personal record for blown saves during the entire 2012 season.[35] Nonetheless, on May 9, 2013 in a game against the San Francisco Giants, Kimbrel earned his 100th save making him the second youngest player in MLB history to reach that mark.[36] With a save against the Cardinals on July 27, 2013, he became only the second Atlanta pitcher after John Smoltz to have three 30-save seasons.[37] Kimbrel surpassed John Smoltz's Braves record of 27 consecutive saves on August 17, 2013.[38]

On September 27, Kimbrel recorded his 50th save of the season in a game against the Philadelphia Phillies. In doing so, he became the 11th pitcher in Major League history to have a 50-save season.[39] He was voted the "GIBBY Awards" Closer of the Year – by the fans, media, team front-office personnel, former players, and SABR.[40]

On February 16, 2014, Kimbrel agreed to a four-year, $42 million extension with the Braves that runs through 2017, with an option for 2018.[41][42] On April 2, Kimbrel tied Gene Garber's 141 saves with the Braves, good for second in franchise history. Two days later, April 4, Kimbrel recorded his 142nd career save, to move into sole possession of second place. On April 25, 2014, Kimbrel became the fastest pitcher ever to reach 400 strikeouts—reaching the mark in 236 innings' worth of work.[43] On June 6, 2014, Kimbrel recorded his 155th save in a game against the Arizona Diamondbacks, surpassing John Smoltz's previous record of 154 saves.[44] On August 29, 2014, Kimbrel recorded his 40th save of the season. He became the third pitcher to reach that single-season milestone in four straight seasons.[a]

On July 8, 2016, Kimbrel injured his knee while taking warmups. The next day, an MRI revealed that there was a tear in the medial meniscus of the left knee. The injury required surgery, and 3-6 weeks to recover.[51] Kimbrel ended his first season with the Red Sox with a 3.40 ERA.

Kimbrel was named the closer for Team USA in the 2013 World Baseball Classic. Despite not surrendering one lead off double all year with the Braves in 2012, Kimbrel gave one up to Nelson Cruz of the Dominican Republic in their round two matchup. Kimbrel would go on to give up two runs in the game, and be the losing pitcher in Team USA's 3–1 loss to the eventual champions.

Kimbrel uses a combination of a four-seam fastball and a power curveball to get outs.[52][53] His fastball averages 96–97 mph and occasionally tops out at 101 mph.[54] His curve, thrown with a "spike" grip, stays in the mid-to-upper 80s. The whiff rate of his four-seamer is 33%, and the curve at is 52%.[55] This combination contributes to a strikeouts per nine innings rate of 14.61 over Kimbrel's career so far (as of 22 July 2015[update]).[56] He is also tied for third among all pitchers from 2002–2012 in the highest percentage of pitches that resulted in swinging strikes.[57]

Kimbrel's four-seam fastball was the 12th-fastest among Major League relievers in the 2011 season. In addition, he threw the hardest curveball, averaging 87 mph. His fastball had the fifth-highest whiff rate among relief pitchers' fastballs (32%), and he also had the highest whiff rate of any reliever's curveball, at better than 55%.[58] His pre-pitch stance has also been widely recognized, and has been dubbed "Kimbreling", or "Spider Arms".[2][59]